[Python-Dev] == on object tests identity in 3.x
steve at pearwood.info
Tue Jul 8 03:58:33 CEST 2014
On Mon, Jul 07, 2014 at 04:52:17PM -0700, Ethan Furman wrote:
> On 07/07/2014 04:49 PM, Benjamin Peterson wrote:
> >Probably the best argument for the behavior is that "x is y" should
> >imply "x == y", which preludes raising an exception. No such invariant
> >is desired for ordering, so default implementations of < and > are not
> >provided in Python 3.
> Nice. This bit should definitely make it into the doc patch if not already
> in the docs.
However, saying this should not preclude classes where this is not the
case, e.g. IEEE-754 NANs. I would not like this wording (which otherwise
is very nice) to be used in the future to force reflexivity on object
To try to cut off arguments:
- Yes, it is fine to have the default implementation of __eq__
- Yes, it is fine for standard library containers (lists, dicts,
etc.) to assume reflexivity of their items.
- I'm fully aware that some people think the non-reflexivity of
NANs is logically nonsensical and a mistake. I do not agree
- I'm not looking to change anything here, the current behaviour
is fine, I just want to ensure that an otherwise admirable doc
change does not get interpreted in the future in a way that
prevents classes from defining __eq__ to be non-reflexive.
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